#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int main() {
    int n;
    scanf("%d", &n);
    long int sum = 0;
    for (int i = n; i > 0; i--)
    {
        sum = sum + i;
    }
    printf("%ld", sum);
    return 0;
}